1. Field of the Invention
The present invention relates to control of reading data from a storage device that stores the data separately in blocks.
2. Description of the Related Art
NAS over SAN is known as one form of systems in which a storage device connected with a network is shared among multiple host computers. NAS over SAN is a technique of storing and reading a file in and from the storage device shared by respective host computers by means of NAS (Network Attached Storage) under SAN (Storage Area Network) environment.
In NAS over SAN, each of the files used by the host computers is stored in blocks defined in the storage device. Relationship between a file and one or plural blocks is managed as meta data. A meta data server for managing the meta data is connected with the network. The storage device, the host computer and the meta data server are connected via relatively cheap communication line, such as Ethernet™. The storage device and the host computer are connected via communication lines, such as Fibre channel that ensures high-speed communication.
The data which has been stored in the storage device is read out in the following sequence. The host computer first specifies the file to be read out and queries the block where the data is stored (Hereinafter referred to as “location”). The meta data server returns the location based on the meta data. Those communications are performed via Ethernet. Then, the host computer requests the storage device to read the data based on the returned location. The storage device provides the host computer with the data stored in the specified block via Fibre channel.
JP2002-108673A and JP1995-73085A disclose examples of system in which a meta data server and a storage device are configured separately. JP2002-23960A discloses an example of the system in which a meta data server is incorporated in a storage device.
In NAS over SAN, improved speed of reading the data from the storage device is required. The storage device is provided with a function of caching the data which has once been read out, however, further improvement is required. Those problems are in common in a system in which the data is read out in files from a storage device that stores the data separately in blocks.